Interpreting paleoclimate from ^l8O and ²H in plant cellulose: comparison with evidence from fossil insects and relict permafrost in southwestern Ontario

Abstract

The oxygen-isotope content of terrestrial plant cellulose is related to that of the source waters by a two-step process involving evapotranspirative leaf-water enrichment and equilibrium isotopic exchange between leaf water and atmospheric carbon dioxide. A combination of two models that describe these steps yields consistent agreement between measured and predicted climatic and isotopic data. Humidity is the dominant influence on variations in the cellulose 18O enrichment relative to the source water. A good first-order approximation of the average daytime relative humidity during the growth season at a site can be based on the linear correlation that exists between humidity and cellulose enrichment, without explicit consideration of factors such as temperature, δ18O of atmospheric vapour, and leaf boundary-layer dynamics.The value of the combined model for paleoclimatic reconstruction has been tested using fossil wood from a late glacial site at Brampton, Ontario. Estimates of the past relative humidity were derived from the divergence between measured δ18O values of fossil wood cellulose and environmental water isotopic compositions inferred from the carbon-bound deuterium contents of the cellulose. Growing conditions were apparently substantially drier than those at present between about 11 500 and 8700 years BP, at a time when coniferous forests predominated in southwestern Ontario. A shift in the inferred meteoric water composition over this period suggests a gradual increase in mean annual temperature of about 2 or 3 °C, in agreement with estimates of temperature change based on paleoentomological data.

Summer maximum temperature in northern France over the past century: instrumental data versus multiple proxies (tree-ring isotopes, grape harvest dates and forest fires)

“…The dependence of δ 18 O and δD on temperature and relative humidity is in agreement with previous results (Burk and Stuiver 1981;Edwards et al 1985;Buhay and Edwards 1995;Feng and Epstein 1996;Baillie et al 2000;Raffalli-Delerce et al 2004;Szczepanek et al 2006). Local temperature has an indirect influence on cellulose δ 18 O and δD, via the precipitation δ 18 O or δD relationship with temperature, but modulated through the evaporation of leaf water.…”

Isotopic studies of leaf water. Part 1: A physically based two-dimensional model for pine needles

“…Leaf water isotopic composition is mainly affected by the isotopic composition of the source water and the relative humidity of the air (Craig and Gordon, 1965;Dongmann et al, 1974), both of which are related to climate conditions. These relationships are the basis for paleoclimate reconstructions using oxygen and/or hydrogen isotopic compositions of tree-ring cellulose (Burk and Stuiver, 1981;Yapp and Epstein, 1982;Edwards et al, 1985;Edwards and Fritz, 1986). More recently, hydrogen isotopic compositions of leaf waxes from lake sediments have been widely studied as records of continental climate (Sauer et al, 2001;Huang et al, 2002Huang et al, , 2004Sachse et al, 2004).…”

18O Spatial Patterns of Vein Xylem Water, Leaf Water, and Dry Matter in Cotton Leaves

“…To date, isotopic values of wood cellulose (Epstein et al, 1977;Yapp and Epstein, 1982;Edwards et al, 1985;Edwards and Fritz, 1986;Roden et al, 2000), grassland phytoliths (Webb and Longstaffe, 2000), and deer bone (Cormie et al, 1994) have been shown to be related to leaf water isotopic composition. Leaf water isotopic signature is not only imprinted on plant organic matter but is also recorded in atmospheric CO 2 and O 2 .…”